1. Field of the Invention
The present invention relates to an electrooptical device having driver circuits consisting of semiconductor devices making use of thin-film semiconductors and also to a method of fabricating such an electrooptical device. More particularly, the invention relates to an active matrix electrooptical device (AMEOD) where a pixel matrix circuit and logic circuitry are integrated on the same panel.
2. Description of the Related Art
In recent years, techniques for fabricating thin-film transistors (TFTs) on an inexpensive substrate have evolved rapidly, because there is an increasing demand for active matrix electrooptical devices. In an active matrix electrooptical device, millions of pixels are arranged in rows and columns. TFTs are arranged at each pixel. Electric charge going into and out of each pixel electrode is controlled by the switching action of each TFT.
Electrooptical devices include liquid crystal displays making use of optical characteristics of liquid crystals, electroluminescent displays employing electroluminescent materials typified by ZnS:Mn, and electrochromic displays exploiting the color changing characteristics of electrochromic materials.
These electrooptical devices are active devices that can be matrix-addressed. High-definition display can be accomplished by utilizing this active matrix construction. As mentioned above, a great feature of the active matrix construction lies in that electric charge going into and out of pixel electrodes arranged in rows and columns within an image display region of an electrooptical device is controlled by turning on and off pixel electrodes disposed at the pixels.
Another feature of the active matrix construction is that driver circuits for driving pixel TFTs are necessary to control pixels. In the prior art technique, a pixel matrix circuit formed on a glass substrate has been connected with a separately prepared driver IC to form an active matrix circuit.
In recent years, however, it has become common practice to form plural circuit TFTs forming driver circuits and a pixel matrix circuit on the same substrate to build driver circuits (known as peripheral driver circuits) around the pixel matrix circuit.
More recently, a system-on-panel (SOP) structure has attracted attention comprising a substrate on which control circuits (e.g., a processor circuit, memory circuits, A/D or D/A converter circuits, correcting circuits, and a pulse-generating circuit) are formed, as well as driver circuits (such as shift register circuits or buffer circuits) for driving pixel TFTs.
A general construction of an electrooptical device is shown in FIG. 3, which gives an example of active matrix liquid crystal display. A pixel matrix circuit 302 is formed on a glass substrate 301. This pixel matrix circuit 302 consists of integrated pixel regions. A portion of the pixel matrix circuit 302 is shown on an expanded scale at 303, where plural regions (two regions in this example) are arranged in rows and columns. At least one pair of pixel TFT/pixel electrode is disposed in each pixel region.
A horizontal scanning driver circuit 304 for transmitting data signals to data lines comprises shift register circuits, level-shifting circuits, buffer circuits, and sampling circuits. The level-shifting circuits amplify driving voltages.
It is assumed that a shift register circuit is operated with 10 V and that a buffer circuit is operated with 16 V. In this case, it is necessary to convert the voltages into other values by a level-shifting circuit. Sometimes, a shift register circuit may be constructed by combining a counter circuit with a decoder circuit. A vertical scanning driver circuit 305 for transmitting gate signals to gate lines comprises a shift register circuit, a level-shifting circuit, and a buffer circuit.
It is expected that a control circuit 306 will be located in the position shown in FIG. 3 in near future. Since the control circuit 306 is composed of complex logic circuitry or memory circuitry such as a processor occupying a large area, it is expected that the total area occupied will increase.
As described above, the pixel matrix circuit 302, the horizontal scanning driver circuit 304, the vertical scanning driver circuit 305, and the control circuit 306 are generally disposed on one glass substrate 301. Accordingly, in order to secure a maximum display area on a given size of glass, it is necessary to minimize the area occupied by circuits other than the pixel matrix circuit.
However, even if the marginal structure as shown in FIG. 3 is adopted, limitations are imposed on increases of the device density of the peripheral driver circuits. Where other values or advantages are added like a control circuit, it is more difficult to increase the area of the pixel matrix circuit.
It is an object of the present invention to provide an electrooptical device, or an optical display device, in which a pixel matrix circuit providing display regions is maximized in area by solving the foregoing problems to thereby accomplish a large area display making full use of the size of the substrate.
An electrooptical device in accordance with the present invention comprises a pixel matrix circuit and logic circuitry formed on the same substrate. The pixel matrix circuit occupies regions in which the logic circuitry is fully or partially disposed.
The present invention also provides an electrooptical device comprising an active matrix substrate having a pixel matrix circuit and logic circuitry thereon. A liquid crystal material layer is held on the active matrix substrate. The pixel matrix circuit occupies regions in which the logic circuitry is fully or partially disposed.
A gist of the present invention lies in an electrooptical device operating in the reflective mode or in the emissive mode. This device is characterized in that pixel regions located on the rear side of the pixel electrodes are effectively utilized. That is, the logic circuitry which would have heretofore been disposed in an outside frame of the pixel matrix circuit as shown in FIG. 3 is totally or partially built into the pixel matrix circuit, by making use of the pixel regions.
A cross section is taken through the active matrix construction on which the pixel matrix circuit is integrated with the logic circuitry. In this cross section, the logic circuitry is fully or partially located below the pixel electrodes connected with the pixel TFTs forming the pixel matrix circuit.
The logic circuitry means circuits other than the pixel matrix circuit consisting of driver circuits and/or control circuits. The control circuits embrace every information-processing circuit necessary to drive an electrooptical device, and are typified by processor circuit, memory circuit, A/D or D/A converter circuit, correcting circuit, a pulse-generating circuit.
Since an electrooptical device operated in the reflective mode (typically, a reflective-type liquid crystal display) does not need to transmit light, it is not necessary to make the pixel electrodes transparent to secure optical paths, unlike the transmissive-type liquid crystal display. Therefore, the rear side of the pixel electrodes (the lower side in the cross section described above) which has been heretofore impossible for the transmissive-type liquid crystal display to utilize can be effectively exploited to dispose the logic circuitry.
The reflective-type liquid crystal display operating in the aforementioned reflective mode is next described briefly by referring to FIGS. 4(A) and 4(B). Shown in FIG. 4(A) are an active matrix substrate 401, a counter substrate 402, and a liquid crystal material layer 403. Pixel electrodes 404 are formed on top of the active matrix substrate 401. If necessary, a reflecting plate may be formed. The pixel electrodes 404 are protected by a protective film 405.
FIG. 4(A) shows the state in which a TFT is OFF. That is, liquid crystal molecules are oriented in such a way that they do not vary the direction of polarization of incident light. Under this condition, an arbitrary direction (in this example, the direction of reflection by a beam splitter 408) of polarization is given to light 407 by a polarizer 406. The light 407 is caused to enter the liquid crystal material layer 403 via the beam splitter 408, which either transmits or reflects the light, depending on the direction of polarization.
As described above, under the condition of FIG. 4(A) (i.e., the TFT is OFF), the light 407 incident on the liquid crystal material layer 403 is reflected by the pixel electrodes 404 such that the direction of polarization is not changed. Then, the light reaches the beam splitter 408. That is, the light 407 reflected by the pixel electrodes 404 is returned with the same direction of polarization as the direction of polarization of the incident light. Therefore, the light 407 hitting the beam splitter 408 is reflected and thus does not reach the observer""s eye.
On the other hand, FIG. 4(B) shows the state in which the TFT is ON. The liquid crystal molecules are oriented so as to polarize light 409 indicated by one arrow. The light 409 reflected by the beam splitter 408 undergoes a change in the direction of polarization by a liquid crystal material layer 410. Then, the light 409 is transmitted through the beam splitter 408 and reaches the observer""s eye.
In this way, the electrooptical device operating in the reflective mode turns on and off light according to whether the TFT is ON or OFF. The reflection-type liquid crystal display is a typical example of such an electrooptical device. Furthermore, electrooptical devices are classified in terms of mode of operation, such as ECB (electrically controlled birefringence effect) mode, PCGH (phase change guest-host) mode, OCB mode, HAN (hybrid alignment nematic) mode, and PDLC guest-host mode (see xe2x80x9cLCD Intelligence,xe2x80x9d August, pp. 51-63, 1996).
However, the present invention can be applied to any type of operation mode as long as a specularly reflecting plate is disposed immediately behind the liquid crystal material layer. Furthermore, the invention can be applied to active matrix electroluminescent displays operating in the emissive mode and to active matrix electrochromic displays exploiting the color changing characteristics of electrochromic materials. That is, the invention can be applied to any kind of structure excluding the transmission-type electrooptical device.
The electrooptical device referred to herein is not limited to a so-called display panel. Rather, the electrooptical device embraces commercial products incorporating display panels. We define the electrooptical device as every device that performs its intrinsic function by electrical action, optical action, or a combination thereof. For the sake of illustration, the xe2x80x9celectrooptical devicexe2x80x9d, may refer either to a display panel or to a final product employing such a display panel.
The present invention also provides a method of fabricating an electrooptical device having a pixel matrix circuit and logic circuitry formed on the same substrate. This method is characterized in that the logic circuitry is totally or partially disposed in regions occupied by the pixel matrix circuit.
The invention also provides another method of fabricating an electrooptical device. This method starts with forming an active matrix substrate having a pixel matrix circuit and logic circuitry on the same substrate. Then, a liquid crystal material layer is formed and held on the active matrix substrate. This method is characterized in that the logic circuitry is totally or partially disposed in regions occupied by the pixel matrix circuit.
An electrooptical device in accordance with the present invention is schematically shown in FIG. 5, where a pixel matrix circuit 502 is integrated with logic circuitry, 503 and 504, on a glass substrate 501. The logic circuitry includes driver circuits and control circuits. The logic circuitry, 503 and 504, overlaps the pixel matrix circuit 502.
This configuration cannot be accomplished by a transmission-type electrooptical device that needs to secure an optical path or opening for passing backlight, for the following reason. Major portions of the pixel matrix circuit of the transmission-type electrooptical device are openings and so it is impossible to build the logic circuitry into the pixel matrix circuit without decreasing the amount of light transmitted.
Accordingly, it can be said that the present invention is a technique capable of being embodied in a reflection-type electrooptical device without the need to secure an optical path. In particular, the logic circuitry is formed below (on the rear side of) the pixel electrodes acting as a reflective plate.
In FIG. 2(A), conductive interconnects, 146-150, act to interconnect circuit TFTs comprising first, second, . . . , the Nth circuit TFTs, thus constructing A/D converters, memory circuits, and so on. Thus, the logic circuitry is completed.
Data lines 152-155 are provided to permit data signals to go into and out of first and second pixel TFTs. It can be said that the data lines 153 and 155 are extraction electrodes for pixel electrodes 160 and 161. The surfaces of these pixel electrodes 160 and 161 are kept specular such that they act as reflective plates for reflecting incident light. If necessary, a reflective film serving as a mirror may be formed over the pixel electrodes 160 and 161.
The structure described thus far enables the logic circuitry, 503 and 504, to be incorporated in the pixel regions forming the pixel matrix circuit 502, as shown in FIG. 5.
Other objects and features of the invention will appear in the course of the description thereof, which follows.